Something like this would work for two tasks in the same page. A more
generic solution would be an interesting challenge but seemingly doable.
Certainly this kind of thing is way more efficient than using explicit
state machines.

context equ 0x20

switch  macro                   ; macro to switch tasks
        movlw $+2               ; load return 'return' address
        goto dispatch
        endm

        org 0
        goto 4
        org 4

        ; init task switcher
        movlw task2             ; 'suspend' task 2
        movw context
        ; fall into task 1

task1   do some stuff
        switch
        do some more stuff
        switch
        etc.
        goto task1


task2   do some stuff
        switch
        blah
        goto task2


dispatch
        xorwf context,f         ; exchange w and context
        xorwf context,w
        xorwf context,f
        movw pcl                ; jump to old context